The invention relates to the automatic control of supply of volatile anaesthetic to a closed circuit at low flow rates.
A closed circuit of anaesthetic is an anaesthetic system based on the re-administration of exhaled gases, from which carbon dioxide has been absorbed, to which oxygen is added and the anaesthetics consumed.
As is known, the concentration of volatile anaesthetic in an anaesthetic circuit is determined by the anaesthetist as he or she wishes and in accordance with the Minimum Alveolar Concentration (M.A.C.) for each anaesthetic.
Changes to this M.A.C. are those which, classically, in a circuit of low flow, are modified by varying the flow of fresh gas and, therefore, the amount of volatile anaesthetic dragged along by the current of fresh gas. This way of controlling the anaesthetic presents some difficulties, among which the excessive consumption of anaesthetic can be mentioned.
Now it has been found that the concentration of anaesthetic can advantageously be regulated by modifying the dial of the anaesthetic vaporiser instead of modifying the flow of fresh gas. This way of controlling the concentration of anaesthetic has, among other advantages, that of reducing the consumption of anaesthetic.